Gauge for measuring inside diameters



Feb. 11, 1958 J. c. ULFELDT GAUGE Foa MEASURING INSIDE DIAMETERS 2Sheets-Sheet Filed Deo. 27, 1954 .10H/v c. UL FELDT,

INVENTOR.

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Feb. 11, 1958 J. c. ULFELDT 2,822,620

GAUGE FOR MEASURING INSIDE DIAMETERS 2 Sheets-Sheet 2 Filed DSC. 27,1954 *y 1 N mm, q m M N JOHN C. ULFELDT ik... INVENTORT ATTORNEY.

Unite This invention re1ates= ton ai gauge: on inside caliper: formeasuring ther inside diameter of arbore? or. th'e llike'and ratesPatent hasa special utility for measuring? the: inside-diameter of abore that'hasfafrestricted'entrance:

TheV problem towhch: the invention is `dir`ectl=dfi-sJ to provide agauge that may` be inserted throug'h there# strictedentrance of theboreandf th'en mayI beexpanded to measure'theinside diameter of thebore'withafhigh degree of accuracy. Onesolutionj forthisiprobleml-istomount a laterally expansible feeler m'eanson'afsiiitable shank memberAWithr means on'l the sha'n'lniernbe-v op"- eratively connected' withthe" feeler meanst'o indicate the extent of.` expansion ofthe feelerme'answhile the feelerv meansr is inY measuring` contactx withj innencircumferential: surface of the bore. *Such-` al solution isinotsatisfactory, howevergbecuseof th'eldifculty of contriv'- inganindicating-means thatwill convey accurate m'e'surementdata from theremote feeler'means: Anyloose' ness, lost motion or backlashv inthelihdicatngl me'chai nisml of such an arrangement is'fataltoi-high'Jaccuracy and, of course, wear on the feeler surfaces* alsdesti'oysaccuracy.

In general, theiinventio'njsolves thisproblemtbymounti ingA anexpansible' feeler' assembly on; a 's lia'nl member with provision forreleasablyxingthe*feeler assembly at whatever length-to'whichrit-mayexpndtand Witlfur# ther'provision for; in elect, folding" thefixedlyexpanded feeler assembly back-onithe"shankmember t`o permitthevshank member with the folded feeler assembly'tqbe withdrawn through therestricted entrance" ofE the* bore: The'iixedly expanded'feelerassembly. is theirmeasured for length by lsuitable" caliper' means'Vv toob'tai'ii de sired inside diameter'measurementofthebore hole'witlexceedinglyhigh accuracy. There isnoindicatingmechl anismwhats'oever tointroduceerr'onland error"'frm wear is completely eliminated by directlyc'aliper'ing the overall length ofthexedly expandedfe'eler assemblyimmediately after each measuring' contactwiththe'inner wall 'surface'ofthe bore.'

A feature of the preferred' practice of "theinventinfis the conceptoflmounting a feeler assembly. on'the end'of the shank member to foldrelative theretc'). by 'rotation about an axis, at an acute angleto-theshank member.- Thisfeature permits the feelervassemblyt belfldedbysimple rotation and such rotatibniV may'ibefachievedl'by manual rotationofwhat maybe trmeda iii-"stilioperatev ing means extendingvalong th'e`shank.. membrt,A the. feeler assembly. d f

The preferredfeeletxi assembly. is (Tshapedwitll'if. two lateralarmsmounted onza stem: portion for radialy extension relative thereto.The two .armscompvrisetwm telef. scoped` tubular members with rasuitablecoiledspring. con* ned'- therein. Yto -urge -the -two :membersIoutward .-longitufv dinally away fromf each othenftSuitablerreleasa-ble:ciampi means' mounted in` the, .stem;portion-.of.theffee1er assembly Yis -adaptedf .to releasablyfvx :onimmobiliaer-thet two` arms lYagainstexpansion' and contractionriat--any'overall2 2,822,26 Patented Feb. 11, 1958 length-f. toA which they maybeY expandedY or. contracted within-the range of measurement of the twoarms. What may loe-termed a second-'operativey means extends' along the:shank member to operate the clamp means at the measuring or' unfoldedposition of the feeler assembly.

The two telescoped tubular. members forming the two arms" are removablyheld to the stem portion of the feeler assembly and canbe removed for.substitutionwith like.v but' different capacity telescoping arms. *Thispermitsfa larger range of bore sizes to behandle'd with the gauge ofthepresent invention.

A further feature of the preferred practice of the invention isttheyconcept of causing the clamp means at its" release position to blockmovement of the feeler assembly out of its measuringposition. Thus whenthe feelerv assembly is expanded in a bore hole tomeasure thelinsidediameter of the bore hole'the feeler assembly cannot befolde'dibaclc'ontlieshank member unless it is first securely fixed in length at thedimensiony of the meias'ureddiameteri'- This `feature eliminates anyerror that may" a-risefiornnadvertent failure to tighten theclampingmeanssecu'rely when a` diameter measurement i`s5tak'en.

The' various" features and advantages of-theV invention willlbejapparent'1f-rbin the following detailed description considered witldie;a'cciorripanying drawings.

Inf' tliediawings; which-are toY be regarded as merely illustra-tive'z`A Figurei'l is a sidef4 elevation of the* presently preferred embodimentof the" gauge showingthe gauge in measuring'position inside av bore holethat has a restricted en"- tr'ance; n

Figure 2 isa fragmentary side elevation of the'handlel portion of thegauge as viewedl along .thelineV 2`2 of Figurel;

Figure 3 is an enlarged longitudinal section' of: the operating end ofthe gauge; n p

Figure 4 is asimilar view of the handle end. of! the gauge; t v

Figure-5 isa face View of abevel'ed gear' ofithe gauge `Figure 6' is asectional'view along the line'A 6-l-'6 of Figure 3 showing a secondbeveledgearof the' gauge mechanism;

Figure 7 isa fragmentary longitdinal'se'ction-taken as indicatedby theline 7-7` of Figure 3`;` I

Figure' 8` is a transverse section taken -as indicated'by the line 8-8of Figure 3; and Y Figure 9'is a fragmentary section similar to Figure 3showing arnodited form of beveled gear that may be used'inthe invention.v

Figure 1 illustrating the preferred embodiment of the invention, showsan inside caliper orv T-shapedv feeler as sembly F mounted on theleadingendofa shankmember`S.- The feeler assembly F is fol'dable onthe'end of the shank member S from a transverse measuring positionshownin solid lines Vinv Figure l to av longitudinal foldedposition outlinedin broken lines. The feeler assembly F may be constructedand mountedinvarious, ways. for. this folding action but, as heretofore ;stated,preferably ismounted on the shank member for rotatiomaboutan inclinedaxis for this purpose; l

The.. shank member S vmayv comprisea relatively long metal ltube 10' anda tubular 'fitting` 12mounted on the leadingfendthereof. As best showninFigure V3, the tubular tttinglZ has anfenlarged end'14- that istelescoped overt-the end of the metal tube 10`an1d is suitablybondedthereto, for example by brazing. The-other end of the tubulariitt-ingwlZis enlarged to form a hemispherical seat;-15-which isflanged to provideasuitablelannularl bearingfsurfaceflG for the 'feeler assembly F. Theaxis of the hemispherical seat i. e. the axis of curvature of theannular bearing surface 16, is inclined at an acute angle relative tothe axis of the shank member S.

The T-shaped feeler assembly F has a stem portion 18 and a diametricalpair of arms 20 and 22 that are adapted for expansion and contraction inoverall length. The stem portion 18 of the feeler assembly is providedwith an integral circular base 24 that is rotatably mounted on thehemispherical seat 15 coaxially thereof. The axis of the circular base24 is inclined at an acute angle relative to the stem portion 18 of thefeeler assembly and this acute angletogether with the previouslymentioned acute angle of the hemispherical seat 15 may totalsubstantially 90. Preferably each of the two acute angles isapproximately 45 The circular base 24 slidingly rests against theannular bearing surface 16 for rotation relative thereto and may be heldin place by a keeper ring 25 that is threaded onto the circular base asshown in Figure 3. The keeper ring slidingly engages the underside of aperipheral flange 26 of the hemishperical seat 15 to hold the circularbase in coaxial position.

Any suitable means may be provided to rotate the base 24 of the feelerassembly F on the hemispherical seat 15. In the present embodiment ofthe invention, what may be termed a rst operating means providedV forthat purpose comprises suitablel gears inside the hemispherical seattogether with tubular means extending through the shank member S foroperation of the gears. In the construction shown, a segmental gear 28having a blank portion 30 is integral with the underside of the feelerassembly base 24 and it is in mesh with a second segmounted inside theshank member S. The tubular member is unitary with an inner tube 36. Inthe construction shown, the tubular member 35 has an inner end portion38 that telescopes into the inner tube 36 and is bonded thereto, forexample, by brazing.

The inner tube 36 extends beyond the handle end of the shank member Sand carries an annular knurled knob 4) which is anchored thereto by apair of set screws 42 (Figure 4). The knurled knob 40 has a tubularshank 44 which may abut a similar tubular shank 45 of a stationaryknurled knob 46 that embraces the shank member S and is suitably bondedthereto, for example by brazing.

It is apparent that rotation of the knurled knob relative to the fixedknurled knob 46 will actuate the segmental beveled gear 32 for rotationof the feeler assembly F on the hemispherical seat 15. 180 of rotationof the circular base 24 on the hemispherical seat 15 will move theT-shaped feeler assembly F from its measuring position shown in fulllines in Figure 1 to its folded position shown in broken lines. Theblank portions of the segmental gears 2S and 32 cooperate to limit therotation of the circular base 24 to this range. Thus at each end of thisrange of 180 the blank portion 34 of the segmental gear 32 abuts theblank .portion 30 of the segmental gear 28. While these two limitpositions may be detected by feeling the resistance to hand rotation ofthe knob 40, preferably suitable index means is provided for visualindication of the unfolded or measuring position of the feeler assemblyF. For this purpose, an index mark 48 (Figure 2) may be placed on theshank 44 of the rotatable knurled knob 4b to register with a similarindex mark 50 on the shank 45 of the stationary knurled knob 46 when thefeeler assembly F is in its transverse measuring position shown in fulllines in Figure l.

Furthermore, the index marks t8 and 50 when aligned are used to indicatethat the feeler arms 20 and 22 are vertically disposed which insuresmore accurate gauging. This is important for it will be remembered thatthese feeler arms will be in many instances not visible to the user ofthe gauge when inserted with the bore undergoing measurement.

As best shown in Figure 3, the stem portion 18 of the feeler assembly Fis integral with a transverse sleeve 52 and the two feeler arms 20 and22 are movably mounted in this sleeve. The two feeler arms 20 and 22comprise a pair of slidingly telescoped tubular members having outer endwalls 54, the outer tubular arm 20 being slidingly mounted in thetransverse sleeve 52 and the inner tubular arm 22 being slidinglymounted in the tubular arm 2t?. Preferably suitable yielding means isconfined by the two tubular arms 20 and 22 to urge the two arms outwardin opposite directions towards their outer limit positions relative toeach other. For this purpose, a coiled spring 55 may be confined incompression between the two end walls 54. Preferably a suitable pin 56is mounted inside the coiled spring 55 to support the spring in itscollapsing or compressing movement and prevent buckling thereof as thearms move together.

As heretofore stated, it is contemplated that a second operating meanswill be provided that will releasably fix or clamp the two feeler arms20 and 22 selectively relative to each other to maintain any giveninside diameter measurement and, of course, such a second operatingmeans must not prevent the folding and unfolding operation of the feelerassembly by the first operating means.

In'the present embodiment of the invention, the second operating meansincludes a suitable clamping screw 58 that isrthreaded axially into thestem portion 18 of the feeler assembly to exert pressure against the twotubular feeler arms 20 and 22 laterally thereof. The clamping screw 58terminates in a tip 60 of reduced diameter that extends through a slot62 in the outer tubular arm 20 and into a keyway 64 in the inner tubulararm 22. It is apparent that when the clamping screw 58 is tightened, thetip presses the-inner tubular feeler arm 22 diametrically towards thesurrounding outer tubular arm 2t) and thus presses both of the two armsdiametrically against the inner circumferential surface of the sleeve52. Thus the clamping screw 58 may be tightened to immobilize the twoarms 20 and 22 relative to each other and relative to the surroundingsleeve 52. The head of the clamping screw 58 is positioned inside thehemispherical seat 15 and is in the form of a hexagonal socket 65.Preferably'the screw head is positioned to back against the face of thesegmental beveled gear 32, as may be seen in Figure 3. Figure 3 showsthe clamping screw 58 in its tightened position at which it clamps orimmobilizes the two tubular arms 20'and 22 relative to each other. Whenthe clamping screw is retracted from this position to release the twotubular arms 20 and 22 for longitudinal expansion movement by theenclosed spring 55, the socket head 65 of the screw backs against thebeveled gear 32.

The range of longitudinal movement of the clamping screw 58 isrelatively small and is such that the tip 60 of the clamping screw stayswithin the keyway 64 of the inner tubular arm 22 throughout the range.Thus the tip 60 of the clamping screw coacts with the keyway and servesas a stop to limit the outward expansion of the two tubular arms 20 and22 relative to each other, the end waliL 66 of the keyway abutting thescrew tip 60 at the outer limit position of the inner tubular arm 22 andthe end wall 68 ofthe slot 62 abutting the screw tip 60 at the outerlimit position of the second tubular arm 20.

The second operating means for releasably immobilizing the two feelerarms 20 and 22 relative to each other further includes a hexagonal rod70 that is slidably and rotatably mounted inside the shank member S forcooperation with the socket head 65 of the clamping screw S8. Thishexagonal rod 70 is integral with a round rod 72, beinga longitudinalextension thereof, and the round rod extends beyond the previouslymentioned inner tube 36. The exposed end of the round rod 72 carries asuitable knurled knob 74 by means of which the round rod and l 5 thehexagonal rod 70 mayfbe manipulated for both. rotation and "longitudinalmovement.

Preferably suitable means is provid'edto limitlongi-,l tudinal movementofthe round rod 72.. ForA this purpose, theperipheryfof the round rodmay be cutaway to provid:` a circumferential .groove .75of `appropriatewidthand one of the set screws'42-may beLformed'with a tip 76 (Figure 4)of reduced diameter torextend through'an aperture 78 in the inner tube36 into the circumferential groove 75. t

It is apparent that theknob.74"may 'be manipulated to shift the endofthe hexagonal rod'70 into and out of the sockethead 65 of the clampingscrew 58 and-may be manipulated for rotation lto tighten and loosen thehclamping screw. It is further apparent ,that when the hexagonal rod'70is retracted out of engagement with the socket head 65 of the clampingscrew 58'r the T-shapedfeeler assembly F is lfree to rotate from itstransverse measura ing position to itsalternateefolded'position.

A feature of the preferred practice ofthe invention is theV concept ofdimensioning the'clampingV screwl 58-in overall length to back againstthe-beveled-gear-SZ as soon as the clamping screw is-retractedsufliciently to lrelease the two feeler arms 20 and 22 for longitudinalexpansion. When the clamping screw 58 is backed-into abutment with thebeveled gear 32 Sit offers frictional resistance to rotation of thefeeler a-ssembly-outof its-measuringposition. Any attempt to rotatethebeveled: gear` 32. for moving the ,feeler assembly F to itsfoldedposition inf creases the frictional resistance of the clampingscrew, since such rotation tends 'to be transmitted to `theclarnpingscrew in a direction to back'the .clamping screw tighter against thebeveled gear. Ifdesired, theA beveledgearz maybe formed. with a slightrecess 80 as shown in Figure 9 to receive the retracted socket head .65of theclarnpiug screw thereby to lock thefeeler assembly in a positivemanner.

The virtue of arranging for the retracted clamping screw 58 to interferewith'v the folding action ofthe feeler assembly in this manner is thatit forces the operator to tighten the clamping .screw securelyl before.the feeler. assembly is moved out of its measuring positionl to its.longitudinal folded position. Thus the invention prevents-anyerrorarising -from inadvertent failure to-tighten the clamping screw in asecure manner. If the clamping screw were not thoroughlytightened, therewould be the possibility of slippage between the two feeler arms 20- and22-in the course of the procedu're of folding the feeler assembly andwithdrawing the feeler assemblyfrom the borehole.

Preferably the hemispherical seat 15 is provided with a closure memberin the form of a screw plug 82 that threads into a circular aperture 84.As shown in Figure 1,. the screw plug S2 is in alignment with the stemportion 18 of the feeler assembly F at the folded position oftheassembly and thus is in alignment with the clamping screw S. It isapparent that with the feeler assembly F in its folded position, thescrew plug 82 may be removed for access to the clampingxscrew.

Thus once the screw plug 82 is removed, a'small tool such as an Allanwrench can be inserted through the opening. 84 and engaged inthe sockethead 65 for rotating the screw 58 to longitudinally retract the tip 60thereof from the keyway 64-and slot 62 to permit. the telescoping armsto be bodily removed from the sleeve 52. It will now be seen'that the.two arms-are demountably carried by the gauge and can be removed forsubstitution with-like but diierent capacity arms.

the tool of thepresent invention by supplying a set of interchangeabletelescoping arms of diierent capacities.

It vshould be mentioned here that the housing formed Thus, a relativelyvwide range of bore sizes may be accurately gauged with" now preferredtoform the same with pasages` 65a through which greasewillfextrude 'astheA rod 70 Vfor example, is moved/into the .socketmthe use ofthe gauge.

The'manner inwhichtheinvention` serves its purpose may be'readilyund'erstood'from the foregoing'. description.

Figure'lfor example, showsla bore. 85 Vhaving anentrance 8'6 ofrestricted cross-sectional dimension. Inpreparatin'for'measurin'g theinsidev diameter ofthe bore 85 fthe'operatormanipulates the knob 40'of.` the rst operating means-to placer the feeler" assemblyl F in`lateral un'- folded' position, andmanipulatesthe knob 74 to loosen theclamping screw 58 by means lof the hexagonal rod 70 therebyltorelease-thetwofeeler arms-20"`and 22;v The operator'then manuallycontractsthe two-feeler 'arms 20 and 22' 'with one hand and` withr theother hand manipulates the knob 7410 tighten'the 'clamping-screwl58'forthe puripose Aof holding the two feelerarms retracted. The knob74 is then manipulated towithdraw the hexagonal yrod170 from '-thesocket head 65 of 'the tightened 'clamping `screw tofree'th'e`feeler-assembly' for folding action. The operator thenk again* rotatesthe knob 40-'oftherst operating means-torotate`thefeeler'assembly' toits folded position:

Withtheefeeler assembly Fsboth contracted and folded',theoperatorinsertsfthei shankmember S with the folded feeler-'assemblythroughrthevrestricted entrance 86 into theboreholelSS 'and thenlrotates the knob 40 of the lrirs't operating meansj to rotate thevfeeler assembly to its -un'' folded measuring position The'l operator*makes sure that the indexline 48-"0nthe shank of the knob 40 registerswith-'thefstationary-index mark- 50 to show that the feeler assemblyis=inl its limit measuring position and that the arms '20?A ZZ'iarevertical.` The operator then manipulates th'e knobl74of the secondoperatingmeans to insert the hexagonalz-rodi70 finto the socket head T65andV lrotates'ethe knob tounscrew and retractthe-clamping-screw 58;' Theretraction of the clamping screw 58 frees the two feeler arms20and22-andthe coiledspring-SS promptly extends thetwo arms into pressurecontact with the inner circumr ferential .'surfaceof the bore 85.

The operator then manipulates the knob l74toreen1" gage the hexagonalrod 70'with the socket head 65-and tightens "the clamping screw. Theknobi74vis then ma` nipulated 'to withdraw the hexagonal `rod7tlfr'om-the socket head -of the clamping'screwandthe knob 40 of thefirst operating means-is manipulatedto fold'k the feeler assembly. Ifthe operator doesnot thoroughly tighten. the clamping screw, he willsense-resistance to the rotation of the knob 40 for'thefoldingaction andwilli thereby be reminded Ytotighten the clampinggscrew thoroughly.

It will be noted that the outer end of the two feeler arms 20 'and 22are suitably rounded to permit the't'wo arms to-be rotated to the foldedposition ofthe'feeler F without any binding action that wouldtend tocome press the two arms and thus result ina'false'measure ment. With thefeeler assembly folded; the operator withdraws the gauge from the borehole throughy the-re stricted .entrance 86and applies an outsidecaliper-f or equivalent measuring device tov ascertain`4 thef-overalllength of the fixedly clamped arms 20.and 22. of the feeler headassembly, this overall length being. the I'true insidediameter of thebore 85.

Althoughv the now preferred embodiment of thepres: entinvention hasbeen. shown. and describedherein,.it is to be understood that theinvention is not to be limited thereto, for it is susceptible to changes'irll formY and detail` within the scope of the appended claims.

`I claim:

l. In a gauge of the character described for measuring the insidevdiameter of a bore hole, the combination of: a shank member havingaleading end; afeeleras- `Vsembly mounted on the leading end of Ysaidlshank mem? ber V-for movement thereon between'a folded'position tovpermit: thegauge-to beV inserted into the bore-hole and a isecond:unfoldedlposition:.extending 'transversely' of the shank,l saidfeeler:` assembly-@being l:."expansible nfits` un' l assenze foldedposition for measuring the inside diameter of the bore hole; yieldingmeans to expand said feeler assembly; a first operating means carried bysaid shank member for manipulation to move said feeler assembly betweenits two positions without affecting the state of expansion of the feelerassembly; and a second operating means carried by said shank member formanipulation to releasably immobilize said feeler assembly againstexpansion by said yielding means, whereby, with the feeler assembly inits unfolded position in measuring contact with the innercircumferential surface of the bore hole, said second operating meansmay be manipulated to x the measuring dimension of the feeler assemblyand then said first operating means may be manipulated to Vfold thefeeler assembly for withdrawal from the bore hole and for subsequentmeasurement to ascertain the inside diameter of the bore hole.

2. A combination as set forth in claim 1 in which said feeler assemblyis mounted on said shank member for rotation on an axis inclined at anacute angle from the axis of the shank member for movement between saidtwo positions; and in which said first operating means rotates thefeeler assembly about said inclined axis.

3. A combination as set forth in claim l in which said second operatingmeans comprises a rst member movably mounted on said shank member and asecond separate member movably mounted on said feeler assembly, said twomembers being operatively engageable with each other at said unfoldedmeasuring position of the feeler assembly to fix the length of thefeeler assembly at whatever measuring length it may assume or to releasethe feeler assembly for expansion and contraction, said two membersbeing disengageable from each other to permit the feeler'assembly to bemoved to its folded position.

4. A combination as set forth in claim 3 in which said second member ismovable by said rst member between an effective position fixing themeasuring dimension of said feeler assembly and a second positionreleasing the feeler assembly for expansion and contraction; and inwhich said second member at its second psition resists movement of saidfeeler assembly from its measuring position to its folded position.

5. A combination as set forth in claim 1 in which said shank member andsaid first operating means are provided with index means to indicatewhen said feeler assembly is at its unfolded measuring position.

6. A combination as set forth in claim l in which said first and secondoperating means are coaxial with each other.

7. In a gauge of the character described for measuring the insidediameter of bore holes, the combination of: a hollow shank member havinga leading end forming a hollow circular seat with the axis of thecircular seat at an acute angle to the shank member; a T-shaped feelerassembly having a stem portion and a pair of feeler arms extendingtransversely at 90 therefrom, said feeler arms being expansible andcontractable in overall length to measure inside diameters of the boreholes, the stem portion of said feeler assembly having a base mounted onsaid seat for rotation about said axis, the axis of said base being atan acute angle from said stem portion, `said two angles totalingsubstantially 90 whereby said feeler assembly is rotatable between afolded position and an unfolded measuring position, at which unfoldedposition the shank member and said stem portion are in alignment witheach other; means in said feeler assembly extending through said shankportion operable to releasably irnrnobilize said feeler arms againstexpansion and contraction thereby to releasably tix the overall lengthof the two arms at measured `inside diameters -of bore holes; operatingmeans carried by said shank member for manipulation to rotate saidfeeler assembly on said seat; and operating means carried by said shankmember and extending into said hollow seat for manipulation to actuatesaid immobilizing means.

' 8. A combination4 as set forth in claim 7 in which said operatingmeans for rotation of the feeler assembly is mounted in said shanklongitudinally thereof and includes gears insidesaid hollow seat forrotation of said feeler assembly.

9. A combination as set forth in claim 7 in which said operating Ameansfor actuating said immobilizing means extends through the operatingmeans that rotates the feeler assembly.

l0. A combination as set forth in claim 7 in which said operating meansfor actuating said immobilizing means is longitudinally movable into andout of operating engagement with the immobilizing means, whereby theoperating means may be manipulated to immobilize said arms at theunfolded measuring position of the feeler assembly and may then belongitudinally retracted out of engagement with said immobilizing meansto permit rotation of the feeler assembly to its folded position.

l1. A combination as set forth in claim 7 in which said hollow seat hasa removable closure in alignment with said stem portion at the foldedposition of the 'feeler assembly for access to said immobilizing means.

l2. A combination as set forth in claim 7 in which said feeler assemblyincludes yielding means to expand said pair of feeler arms into contactwith the wall of a bore hole.

13. A combination as set forth in claim 12 in which one of said armstelescopes over the other arm with said yielding'means inside the twoarms; and in which said immobilizing means is in the form of a screw toexert clamping pressure on the two telescoped arms.

14. A combination as set forth in claim 13 in which said screw meansextends through a longitudinal slot in the outer arm into contact withthe inner arm to press the inner arm in one diametrical directionagainst the outer arm.

15. A combination as set forth in claim 14 in which said screw means inits retracted release position engages the wall of said seat to resistrotation of said feeler assembly out of its measuring position.

16. In a gauge of the character described for measuring the insidediameter of bore holes, the combination of: a tubular shank memberhaving a leading end forming a hollow circular seat having its axis atan acute angle to the shank members; a T-shaped feeler assembly having astem portion and a pair Aof feeler arms extending transversely attherefrom, said feeler arms being expansible and contractable in overalllength to measure inside diameters of bore holes, the stem portion ofsaid feeler assembly having a base mounted on said seat for rotationabout said inclined axis, lthe axis of said base being at an acute anglefrom said stern portion, said two angles totaling substantially 90whereby said feeler assembly is rota-table between a folded position andan unfolded measuring position, at which unfolded measuring position theshank member and said stern portion are in alignment with each other; agear in said hollow circular seat integral with said base; a second gearin said seat in mesh with said first mentioned gear; a tubular operatingmeans rotatably mounted in said shank coaxially thereof in operativeengagement with said second gear, said operating means having a portionexposed for manipulation to rotate said feeler assembly between its twopositions; yielding means in said feeler assembly to expand said twoarms radially outward from said stem portion for measuring the insidediameters of bore holes; rotatable means in said feeler assemblyextending through said shank portion to releasably immobiliz-e saidfeeler arms against expansion and contraction thereby to releasably tixIthe overall length of the two arms at measured inside diameters of boreholes; and

an operating member mounted in said operating means ooaxially thereoffor operative engagement with said immobilizing means, said operatingmember having a portion extending outside of said operating means formanual manipulation, said operating member being movable 1ongitudinallyfor retraction out of engagement with said immobilizing means to permitmovement of said feeler assembly out of its unfolded measuring position.

References Cited in the le of this patent UNITED STATES PATENTS GardnerMar. 27, 1951 FOREIGN PATENTS Great Britain June 27, 1887 Germany July31, 1936

